title: Positron emission tomography imaging of CD105 expression during tumor angiogenesis.
abstract: OBJECTIVE
  Overexpression of CD105 (endoglin) correlates with poor prognosis in many solid tumor types. Tumor microvessel density (MVD) assessed by CD105 staining is the current gold standard for evaluating tumor angiogenesis in the clinic. The goal of this study was to develop a positron emission tomography (PET) tracer for imaging CD105 expression.
  
  
  METHODS
  TRC105, a chimeric anti-CD105 monoclonal antibody, was conjugated to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and labeled with (64)Cu. FACS analysis and microscopy studies were performed to compare the CD105 binding affinity of TRC105 and DOTA-TRC105. PET imaging, biodistribution, blocking, and ex vivo histology studies were performed on 4T1 murine breast tumor-bearing mice to evaluate the ability of (64)Cu-DOTA-TRC105 to target tumor angiogenesis. Another chimeric antibody, cetuximab, was used as an isotype-matched control.
  
  
  RESULTS
  FACS analysis of human umbilical vein endothelial cells (HUVECs) revealed no difference in CD105 binding affinity between TRC105 and DOTA-TRC105, which was further validated by fluorescence microscopy. (64)Cu labeling was achieved with high yield and specific activity. Serial PET imaging revealed that the 4T1 tumor uptake of the tracer was 8.0 ± 0.5, 10.4 ± 2.8, and 9.7 ± 1.8%ID/g at 4, 24, and 48 h post-injection, respectively (n = 3), higher than most organs at late time points which provided excellent tumor contrast. Biodistribution data as measured by gamma counting were consistent with the PET findings. Blocking experiments, control studies with (64)Cu-DOTA-cetuximab, as well as ex vivo histology all confirmed the in vivo target specificity of (64)Cu-DOTA-TRC105.
  
  
  CONCLUSIONS
  This is the first successful PET imaging study of CD105 expression. Fast, prominent, persistent, and CD105-specific uptake of the tracer in the 4T1 tumor was observed. Further studies are warranted and currently underway.
authors.affiliation: Department of Radiology, University of Wisconsin - Madison, Madison, WI 53705-2275, USA.
authors.forename: Hao
authors.initials: H
authors.lastname: Hong
authors.forename: Yunan
authors.initials: Y
authors.lastname: Yang
authors.forename: Yin
authors.initials: Y
authors.lastname: Zhang
authors.forename: Jonathan W
authors.initials: JW
authors.lastname: Engle
authors.forename: Todd E
authors.initials: TE
authors.lastname: Barnhart
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Nickles
authors.forename: Bryan R
authors.initials: BR
authors.lastname: Leigh
authors.forename: Weibo
authors.initials: W
authors.lastname: Cai
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000276:immunology; D015703:Antigens, CD / Q000276:immunology / Q000378:metabolism*; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000503:physiopathology*; D045744:Cell Line, Tumor; D003301:Copper Radioisotopes; D000071063:Endoglin; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry; D006801:Humans; D051379:Mice; D009389:Neovascularization, Pathologic / Q000000981:diagnostic imaging* / Q000378:metabolism*; D049268:Positron-Emission Tomography / Q000379:methods*; D011956:Receptors, Cell Surface / Q000276:immunology / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D003301:Copper Radioisotopes; C064206:ENG protein, human; D000071063:Endoglin; D006573:Heterocyclic Compounds, 1-Ring; D011956:Receptors, Cell Surface; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid